# Maths help integration

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#1

Can someone explain where I went wrong pls
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2 weeks ago
#2
Looks like a tan() type substitution to me.
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2 weeks ago
#3
I think you forgot to integrate what’s inside the bracket?
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2 weeks ago
#4
(Original post by mqb2766)
Looks like a tan() type substitution to me.
Yeah, It looks like an arctan(x) outcome somewhere along the line..
Yazomi; don't remove the fraction and make it a negative power - that may be helpful to do
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#5
(Original post by mqb2766)
Looks like a tan() type substitution to me.
(Original post by ㅋㅋㅋㅋㅋ)
I think you forgot to integrate what’s inside the bracket?

Hmm after tan substitution I got

And I think the answers a bit dodgy
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2 weeks ago
#6
(Original post by Yazomi)
Hmm after tan substitution I got

And I think the answers a bit dodgy
I don't even know what you're doing there!

Your initial integral was in terms of x, so I would expect you to set and proceed from there. Where did u come from?
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#7
(Original post by ThatsAGoodOne349)
Yeah, It looks like an arctan(x) outcome somewhere along the line..
Yazomi; don't remove the fraction and make it a negative power - that may be helpful to do

I’m not sure if this is what you mean but I’ve got this instead?
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#8
(Original post by davros)
I don't even know what you're doing there!

Your initial integral was in terms of x, so I would expect you to set and proceed from there. Where did u come from?

Here’s the question is it helps
I was trying to do part be but I was trying to see if I could still find out the area without using the cos^2 theta given.

I think the part I messed up was trying to figure out what to put u=
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2 weeks ago
#9
(Original post by Yazomi)

I’m not sure if this is what you mean but I’ve got this instead?
That is even worse than your original attempt!

I don't mean to be rude, but how long have you been studying integration? Are you getting support from a teacher or self-studying?

You've posted a number of integration questions recently where you seem to have invented rules for integration that just aren't valid, instead of following standard methods like recognition, substitution and IBP. This is leading you into all sorts of problems later on
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2 weeks ago
#10

Let , then

The integral becomes;

To integrate cos^2, you need double angle identity.
Last edited by RDKGames; 2 weeks ago
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2 weeks ago
#11
(Original post by Yazomi)

Can someone explain where I went wrong pls
https://www.integral-calculator.com/ this shows you how to solve integrals step by step

Also man you gotta relearn integration from the ground up. I don't know how you're going from int((1+x^2)^-2)dx to -(1+x^2)^-1 + c but, in the nicest way possible, it shows that there are serious gaps in your understanding of how integration works. At this point you're inventing your own rules for integration, which aren't even remotely correct. Try TLMaths, ExamSolutions, Zeeshaan Zamurred, or some other maths teacher who makes videos on youtube, whoever you vibe best with.

EDIT: looking at a more recent post, my man this is worse than not understanding integration. Go back to GCSE maths, I'm not trying to be mean but if you don't understand fractions how are you going to be able to do integration?
Last edited by Filthy Communist; 2 weeks ago
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#12
Oh dear welp I’ll start practising some more. I don’t think I’ll be prepared for the mock tmr 😂
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2 weeks ago
#13
(Original post by Yazomi)
Oh dear welp I’ll start practising some more. I don’t think I’ll be prepared for the mock tmr 😂
The cheatsheet
is decent, but an aid rather than substitute for practice.
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#14
(Original post by mqb2766)
The cheatsheet
is decent, but an aid rather than substitute for practice.
Ahhh thankssss it’s looking really helpful so far
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2 weeks ago
#15
(Original post by Yazomi)
Ahhh thankssss it’s looking really helpful so far
It's a bit basic, but something to build on.
When you think you've done the indefinite integrals, try differentiating them to check it gives the original function, if you've got time.
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2 weeks ago
#16
And also note you can instantly check definite integrals with your calculator, assuming you cave the 991-EX or CG-50

It does it numerically, so it will give a decimal answer. Subtract that answer from what you got and if you get 0 you did it right.
Last edited by Filthy Communist; 2 weeks ago
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#17
(Original post by Filthy Communist)
And also note you can instantly check definite integrals with your calculator, assuming you cave the 991-EX or CG-50

It does it numerically, so it will give a decimal answer. Subtract that answer from what you got and if you get 0 you did it right.
Alright got ya thanks

(Original post by mqb2766)
It's a bit basic, but something to build on.
When you think you've done the indefinite integrals, try differentiating them to check it gives the original function, if you've got time.
Just got one more quick question

For a question like this how do you know what to use as a substitute or it’s really just guess work?
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2 weeks ago
#18
(Original post by Yazomi)
Alright got ya thanks

Just got one more quick question

For a question like this how do you know what to use as a substitute or it’s really just guess work?
1-x^2 sounds like the Pythagorean identity, as the limits also hint at (30-60-90 triangle). So something like cos^2 + sin^2 = 1 gives
cos^2 = 1 - sin^2

1+x^2 hints at:
1 + tan^2 = sec^2
Last edited by mqb2766; 2 weeks ago
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#19
(Original post by mqb2766)
1-x^2 sounds like the Pythagorean identity, as the limits also hint at (30-60-90 triangle). So something like cos^2 = 1 - sin^2

1 x^2 hints at:
1 tan^2 = sec^2
What on earth
！(◎_◎; )
Ok I’ll leave that for later. I don’t think I’ll be able to take on or even spot these hints in the actual thing
Last edited by Yazomi; 2 weeks ago
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2 weeks ago
#20
(Original post by Yazomi)
What on earth
！(◎_◎; )
Ok I’ll leave that for later. I don’t think I’ll be able to take on or even spot these hints in the actual thing
Thats fine, but these trig substitution questions come up a fair bit. There are only a few trig identities that frequently come up, so it's worth getting your head round them after tomorrow.
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